Noise level outputs and use with RM 4014 to generate percussive sound

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eljay
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Noise level outputs and use with RM 4014 to generate percussive sound

Post by eljay » Wed Aug 19, 2020 3:47 pm

I've been putting together a patch to emulate the ubiquitous Pink Floyd track 'On the Run', why, because it has to be done and I was keen to get something sounding close to the original. I'm pleased with the initial results particularly now I'm using the Diode Ladder Filter which gives a very similar tonal quality.

I have employed the use of the Oakley Ring Modulator and a noise source to generate the percussive 'high-hat' sound. I read or saw somewhere that this was generated on the EMS AKS by feeding in the sequence CV to one ring-modulator input and a noise source into the other. After trial and error I've got it to work using the Oakley RM 4014 (sequencer CV into X (AC only), Noise into Y(DC or AC), both X and Y level pots at maximum, Y offset has no effect. I don't know why only this configuration works, but it does, or indeed why it works at all.

More importantly, if I use the output from my Oakley Noise module (White or Pink) I hear nothing, if I use the Noise output from my Oakley Sample/Slew module it works but is very faint, and the source that works best and sounds like it's supposed to albeit a little quieter than I would like is the Clipped noise output from the Sample/Slew module which as I understand is 'soft-clipped' to a 5V peak.

My question is, why am I seeing this discrepancy using different noise sources (I also tried using a noise source from a Eurorack module which also didn't work) do I need to re-calibrate the output from my Noise module(s) or is there a problem with my Ring Modulator? All my modules are DIY so there is possibility that I haven't set something up correctly or it's drifted out over the three years since I built most of it.

Any feedback/suggestions appreciated.

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Synthbuilder
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Re: Noise level outputs and use with RM 4014 to generate percussive sound

Post by Synthbuilder » Thu Aug 20, 2020 2:20 am

eljay wrote:
Wed Aug 19, 2020 3:47 pm
I read or saw somewhere that this was generated on the EMS AKS by feeding in the sequence CV to one ring-modulator input and a noise source into the other.
The AKS has only one proper VCA. There are others like the resonance control, but you can't access these individually. So to get the extra one they used the AKS's ring modulator. Any modern ring modulator, ie. not the diode ring type designs which give the ring mod its name, is a four quadrant multiplier. This is essentially two VCAs bolted together; one to handle positive CVs, the other to handle negative CVs. If you only put a positive voltage into the Y input, and set it to DC, the 4014 will behave like any standard VCA. So simply connecting a noise output to the X input and turning up Y offset should allow you to hear the noise at a level determined by the Y offset control. If this doesn't happen your 4014 is broken.

But the AKS's ring mod is AC coupled on both inputs which means you can't use it as a standard VCA. Any slow moving control voltage is essentially filtered out. However, a fast moving sequencer line is a bunch of differing voltage steps. These will be differentiated by the capacitors that provide the AC coupling in the AKS's ring mod. What this means is that you'll get a stream of little pulses each time the sequencer steps to a new level. Those could well be of the right size to behave like an envelope generator and open and close the VCA part of the ring mod. Thus giving you the hi-hat part.

Now if you've already played around with an Oakley RM4014 and you've not got the effect you want I suspect the two ring mods are sufficiently different so it'll not work.

You could try this if you have an Oakley Noise/Filter.

Patch the white noise into the X input of the RM4014. Set to X input to AC and turn up full.
Patch the sequencer CV into the HPF input of the Noise/Filter.
Patch the output of the HPF to the Y input of the RM4014. Set to Y input to DC and turn up full. The Y offset should be left at zero.
Run sequence and tweak the HPF cut off to taste. It'll probably be quite quiet.

That may, or may not, produce something like you want.

Something to bear in mind, nothing quite sounds like a Synthi other than another Synthi, and even that's not guaranteed.

The Synthi (AKS or VCS3) is a mash up of good quality and poor quality parts. An oddball of ingenuity, and downright bad and unusual design choices. It is indeed limited and unstable, the power supply is poor (particularly the first versions) and there is no temperature compensation on the VCOs and VCF (although this can be added). The matrix is noisy and adjacent channels bleed into one another. The audio pathway readily overloads and clips. And the internal loudspeakers are dreadful.

And yet...

It is a wonderful instrument to use and play with. It takes you in completely different directions to conventional synths. And if you are dyslexic like me and really struggle with pin matrices, you can end up with the most bizarre happy sonic accidents.

Tony

eljay
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Re: Noise level outputs and use with RM 4014 to generate percussive sound

Post by eljay » Thu Aug 20, 2020 4:48 am

Thanks for the informative reply Tony it is very helpful. I have re-tried using the Noise module White Noise output and connecting to the RM4014 as you describe and I can now get the percussive effect I was expecting, the noise output from the Sample/Slew module also works. The output levels are very low using those White noise sources and I still get the best output from the RM using the Clipped output from the Sample/Slew as the noise source.

I tried your suggestion with the Noise Filter using the HPF CV input but couldn't generate anything of any clarity or volume, but good to try. In conclusion, the Sample/Slew Clipped output is the best noise source for this particular application and is seems to work extremely well using the RM inputs as you describe.

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Synthbuilder
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Re: Noise level outputs and use with RM 4014 to generate percussive sound

Post by Synthbuilder » Thu Aug 20, 2020 6:45 am

eljay wrote:
Thu Aug 20, 2020 4:48 am
I tried your suggestion with the Noise Filter using the HPF CV input but couldn't generate anything of any clarity or volume, but good to try.
Just in case you tried the wrong thing. In my patch suggestion, the sequencer CV should be connected to the HPF IN. Nothing needs to be be connected to the CV IN input of the Noise/Filter input.

I think the clipped noise works better because it is, on average, a more powerful audio signal.

Another thing that might help is amplify the sequencer CV before putting it into the ring mod (or HPF and then RM). If you're using the Oakley Sequencer, use the CV2 output and turn up its level to full. The VCOs can be controlled by CV1.

eljay
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Re: Noise level outputs and use with RM 4014 to generate percussive sound

Post by eljay » Thu Aug 20, 2020 7:30 am

Thanks Tony for the clarification, I had used the CV input to the Noise Filter. I've tried again putting the sequencer CV into the HPF and I can get it to work using the method you describe but it is very quiet so I'll stick with the Clipped output from the Sample/Slew.

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